I. Field of the Invention
The invention relates generally to navigation based on image processing, and more specifically to determining an orientation of a personal navigation device, relative to a moving vehicle, for interpreting accelerometer and gyrometer measurements.
II. Background
Position estimates are often provided by receiving and processing satellite positioning signals. When satellite signals are not available, a mobile device resorts to dead-reckoning techniques to estimate incremental positioning updates. Usually, dead-reckoning techniques rely on measurement data from inertial sensors (e.g., accelerometers and gyrometers). Such inertial sensors must be frequently calibrated to maintain reliable measurements. For example, when an accelerometer detects no acceleration besides gravity, the mobile device may be presumed stationary at which time the gyrometer is eligible to be calibrated. Even with frequent recalibration, inertial sensors provide sensor measurements with some inherent error. These errors accumulate over time and, if the sensors are left un-calibrated, at some point position estimates provided by dead reckoning will no longer be reliable. An improved method and device are needed to reduce these inherent errors.